Flight management systems have evolved to a level of sophistication that helps flight crews fly commercial airplanes more safely and efficiently.

20 aero quarterly qtr_02 | 09 Contribution of Flight Systems to Performance-Based Navigation

Flight Management Systems (FMS) and associated airplane flight systems are the primary navigation tools on board today’s commercial airplanes. The evolution of these systems has led the way for performance-based navigation (PBN) and the U.S. Federal Aviation Administration’s (FAA) Next Generation Air Transportation System.

By Sam Miller, Associate Technical Fellow, Flight Deck, Flight Crew Operations

PBN is a concept used to describe naviga­ concept is made possible largely by aviators to fly coast to coast across the tion performance along a route, procedure, advances in the capabilities of airplane FMS. United States. However, these early flights or airspace within the bounds of which This article helps operators better were filled with uncertainties and their use the airplane must operate. For transport understand how the FMS and other of visual flight rules soon gave way to airplanes, it typically is specified in terms airplane flight systems have evolved over reliable attitude indicators and ground- of required navigation performance (RNP). time, how they contribute to PBN opera­ based navigation aids, or navaids. Non- The PBN concept defines navigation tions, and plans for further advancement. directional radio beacons and the airplane’s performance in terms of accuracy, integrity, airborne automatic direction finder equip­ availability, continuity, and functionality. ment allowed aviators to “home in” on the Air navigation tools leading up These operations provide a basis for to the FMS beacon and navigate reliably from station to designing and implementing automated station. Non-directional radio beacons are flight paths that will facilitate airspace design, still being used today throughout the world. Early aviators relied on very basic instru­ terminal area procedure design, traffic flow In the 1940s, the introduction of a mentation to keep the airplane upright and capacity, and improved access to runways radio-magnetic indicator or dual-bearing navigating toward the desired destination. (more information about PBN can be found distance-heading indicator facilitated the Early “turn and slip” indicators and ground in AERO second-quarter 2008). The PBN use of ground-based navaids, including references such as lighted beacons enabled

21 WWW.boeing.com/commercial/aeromagazine Figure 1: Typical VOR installation By 1952, more than 45,000 miles of airways using the VOR were in operation. A DME transmitter was usually located on the ground with VOR 15 DME stations. DME transmitters would respond to interrogation by transceiver equipment installed on airplanes and provide the pilot with a reliable 360º distance in nautical miles to the transmitter. Pilots operating in areas where VOR and DME coverage was available had both distance and course 270º 90º information readily available. 270-degree Radial

180º

VOR/DME

the very-high-frequency omni-directional on the 727, 707, and 747-100. During this While Boeing was continuing work on range (VOR) navigation system and dis­ same time, Collins produced the AINS-70, new commercial airplane navigation systems tance measuring equipment (DME). VORs an area navigation (RNAV) computer on the for the new “glass” flight decks, a debate came into wide use in the 1950s and DC-10. Each of these steps reduced the was under way among the airlines about quickly became the preferred navigation amount of interpretation by the flight crew the need for a dedicated flight engineer radio aid for flying airways and instrument by presenting more specific indications of crewmember. In July 1981, an industry task approaches (see fig. 1). VOR and DME airplane positional and situational status. force determined that two-crew operation provided the framework for a permanent Even so, the reliance on the flight crew to was no less safe than three-crew operation. network of low-altitude victor airways manually interpret and integrate flight This decision would have a profound effect (e.g., V-4) and high-altitude jet routes information still provided opportunities for on the design of all Boeing commercial (e.g., J-2), which are still in place today. operational errors. airplanes, including a short-notice imple­ Long-range navigation over remote mentation for the new 767. With one fewer and oceanic areas, where navigation radio crewmember, Boeing engineers focused on The first integrated flight transmitters did not exist, was originally management computer a flight deck design that would reduce crew accomplished by dead reckoning and workload, simplify older piloting functions, celestial navigation. The introduction of the and enhance flight deck efficiencies. When Boeing began work on the 767 inertial navigation system (INS) on airplanes The early 767 FMC provided airplane airplane program in the late 1970s, the facilitated long-range capability by providing performance predictions using stored company created a flight deck technology a continuous calculation and display of the airframe/engine data and real-time inputs group with engineers dedicated to the airplane’s position. Flight crews could enter from other onboard systems, such as the development of the flight management waypoints and the INS would calculate air data computer and inertial reference computer (FMC) and the control display heading, distance, and estimated time of system (IRS). This performance function unit (CDU) (see fig. 2). Boeing merged arrival to the respective waypoint. replaced flight crew back-of-the-envelope- previous designs of the performance At the same time, the 1970s fuel crisis type estimates with relatively precise time management computer and the navigation provided the drive to optimize navigation and fuel predictions based upon actual computer into a single FMC that integrated capabilities in commercial airplanes. As airplane performance parameters, such as many functions beyond navigation and a result, avionics manufacturers began gross weight, speed, altitude, temperature, performance operations. The company producing performance management and winds. used experience gained from Boeing’s other computers and navigation computers to Then, as now, the navigation function research projects to develop advanced help operators improve the efficiency of was based on the IRS position and used implementations of performance manage­ their airline operations. Boeing’s initial entry ground-based navaids (e.g., DMEs, VORs, ment functions and navigation into a into this arena was represented by the localizers) to refine the IRS position and single FMC. The new FMC system was implementation of the early Sperry (now correct for IRS drift. A navigation database envisioned as the heart of an airplane’s Honeywell) automatic navigation systems (NDB) was included in the FMC’s memory flight planning and navigation function.

22 aero quarterly qtr_02 | 09 Figure 2: 757/767 FMC CDU One of the first implementations of an FMC CDU was designed for the 757 and 767 in the early 1980s.

and contained approximately 100 kilobytes For several years following the initial of data consisting of navaids, airways, FMS certifications, minor changes were approach procedures, and airports. The made to enhance the FMS operation, NDB allowed flight crews to easily enter but no significant hardware or software flight plans from takeoff to landing and changes were made until the early 1990s. make real-time route changes in response to air traffic control (ATC) clearances. The Developing the modern FMC FMC also provided guidance to the flight plan route using the lateral navigation (LNAV) In the late 1980s and 1990s, the airline and vertical navigation (VNAV) functions. industry requested the capability of direct Initially, the FMC was equipped with LNAV routing from one location to another, only. VNAV was a new challenge and without the need to follow airways based required a significant effort on the part upon ground-based navaids. Modern of Boeing and Sperry (now Honeywell) FMS equipped with a multi-sensor navi­ engineers to make the vertical guidance gation algorithm for airplane position component operational. determi­nation using VOR, DME, localizer, After the development of the 757 and and IRS data made this possible, and 767, Boeing also worked with Smiths RNAV was transformed from concept to Aerospace (now GE Aviation) to develop operational reality. an FMC as part of a major update to the But oceanic operations and flight 737 family. The operation of the 737 FMC, over remote areas — where multi-sensor the appearance of the CDU, and the CDU updating of the FMC could not occur menu structure were designed to parallel with accuracy better than the drift of IRS those on the 757 and 767. The FMC systems — made RNAV operations difficult. became part of the design of the 737 Operations in these areas of the world were Classic family, which included the 737-300, increasing during the 1990s, and there was 737-400, and 737-500. The 737-300 was pressure on avionics suppliers, airplane the first of the family to be certified in 1984. manufacturers, and regulatory agencies Boeing offered the 737 Classic family with to find a way to support precise navigation either single or dual FMCs and with either in remote and oceanic areas. As a result, the traditional electro-mechanical attitude the concept of a future air navigation director indicator/horizontal situation system (FANS) was conceived in the early indication flight instrument suite or the 1990s (see AERO second-quarter 1998). EADI/EHSI “glass” flight deck derived Subsequently, Boeing and Honeywell from the 757/767 design. introduced the first FANS 1-capable FMC

23 WWW.boeing.com/commercial/aeromagazine An RNP system should contain both performance monitoring and alerting: a caution alert is initiated by the FMC and annunciated on the display system to draw flight crew attention in the event that ANP exceeds RNP.

on the 747-400. At the heart of the system to the flight crew when this containment RNP: enabler of PBN was a new, more capable FMC that might not be assured. GPS was originally implemented several new operations: a military navigation sensor that was The concept of a reliable and repeatable allowed for commercial use with some defined path with containment limits n Airline operational communications — limitations. Integrated as the primary FMC was not new. Early conceptual work was Digital communication of data (data link) position update sensor, GPS provided done at the Massachusetts Institute of such as flight plans, weather data, and exceptionally precise position accuracy Technology in the 1970s, but the modern text messaging directly from the airline compared to ground-based sensors and FMC, with its position accuracy and operations facility to the FMC. enabled the FMC’s capability for precise guidance algorithms, made reliable path n Controller-pilot data link communica­ navigation and path tracking. GPS remains maintenance practical. tions — Digital communication between the primary sensor for the current gener­ The first demonstration of the FMC’s ATC and the airplane in the form of ation FMCs. Data link provided a reliable terminal area precision came at Eagle, predefined messages. method of digital communication between Colorado, in the mid-1980s. A team com­ n Automatic dependent surveillance — the airplane and the air traffic controller. prising American Airlines, the FAA, and Information about position and intent A comprehensive list of preformatted Sperry (now Honeywell) applied RNP-like generated from an ATC request. messages was implemented­ to provide for principles to approach and departure n Global positioning system (GPS) — efficient traffic separation referred to as procedures to the terrain-challenged Incorporation of satellite navigation controller-pilot data link communications. runway. Following simulator trials, the functions in the FMS for the primary Concurrent with the FANS 1 FMC, procedures were successfully flown into means of navigation. Alaska Airlines teamed with Boeing, Smiths Eagle and subsequently approved by the n Air traffic services facilities notification — Aerospace (now GE Aviation), and the FAA. The result: reliable approach and ATC communication protocol initialization. FAA to develop procedures that would departure procedures that provide improved n RNP — A statement of the navigation provide reliable access to airports that access to Eagle. performance necessary for operation are sur­rounded by difficult terrain. By Although Eagle demonstrated the FMC’s within a defined airspace. virtue of the surrounding rough terrain, capability to execute precisely designed n Required time of arrival — Enablement of the Juneau, Alaska, airport became the terminal area procedures, in the mid-1980s, airplane performance adjustments to prime candidate for the certification effort. it would take another 10 years until RNP meet specified waypoints at set times, Because the approach to runway (RW) 26 equipment was available for airline oper­ when possible. was the most challenging air corridor to ators. The FMC’s navigation position Although each feature was individually Juneau, it was selected as the most accuracy enhanced with GPS and lateral significant, the three primary enablers for rigorous test to prove the real performance and vertical guidance algorithms, the FANS operations were RNP, GPS, and data capability of RNP (see fig. 3). development of the vertical error budget, link. RNP defined the confines of the lateral In 1995, Alaska Airlines successfully and additions to crew alerting enabled route, and the FMC provided guidance to demonstrated its ability to safely fly airplanes RNP and its future applications. reliably remain on the route centerline. The to RW 26 using RNP and soon began RNP is a statement of the navigation FMC’s RNP function also provided alerting commercial operations using RNP, which performance necessary for operation within was a first for commercial aviation.

24 aero quarterly qtr_02 | 09 Figure 3: Juneau, Alaska: Site of initial RNP certification efforts RNP enabled an approach to runway 26 and access to Juneau that in some weather conditions was not otherwise practical.

a defined airspace. The FMC’s navigation track error is displayed on the FMC’s reasonably robust for the initial RNAV and function ensures containment within the “PROGRESS” page or under the naviga­ RNP operations, but each of the Smiths defined airspace by continuously computing tional display’s airplane symbol when NPS (now GE) and Honeywell FMCs on Boeing the airplane’s position. The FMC’s actual is on board. The display provides flight airplanes continued to be updated with navigation performance (ANP) is the com­ crews with a precise assessment of lateral software improvements and new hardware puted navigation system accuracy, plus the deviation, particularly important in low versions with enhanced processing power associated integrity for the current FMC RNP environments. Display of cross-track and memory. Some enhancements position. It is expressed in terms of nautical error on the “PROGRESS” page was an specifically related to RNP include: miles and represents a radius of a circle original feature in the Boeing FMCs and n Vertical RNP — Introduced the capability centered on the computed FMC position, continues as a fundamental indication with which to define containment relative where the probability of the airplane of path deviation. to the computed VNAV path (see fig 5). continuously being inside the circle is Although RNP operations are increasing n Radius to fix legs — Implemented the 95 percent per flight hour. in numbers and applications and will provide ARINC 424 leg type that provided a fixed Boeing flight decks display both ANP for the future for PBN, RNAV is also being radius ground path (similar to a DME and RNP. With the advent of the navigation increasingly implemented for operations arc but without the required navaid). performance scales (NPS) and associated where consistent ground tracks are desired. n En-route fixed radius transitions — display features, RNP and ANP are RNAV approaches, standard instrument Implemented a fixed radius transition digitally displayed on the navigation display. departures (SID) and standard terminal between en-route path segments, to Additionally, and as defined in regulatory arrival (STAR) procedures are being enable the implementation of reduced guidance, an RNP system should contain produced primarily throughout the United route spacing in higher-density traffic both performance monitoring and alerting: States and in selected areas of the world. environments (currently 737 only). a caution alert is initiated by the FMC and RNAV leverages the original path manage­ n GPS availability — Refined algorithms annunciated on the display system to draw ment capability of the FMC and, unlike that enhanced the navigation perfor­ flight crew attention in the event that ANP RNP, lateral containment was not specified. mance for very low RNP procedures. exceeds RNP. That alert typically signifies From an operational point of view, RNP is n LNAV tracking — Enhanced the pre­ that the performance of an FMC position RNAV with containment. If a path is defined cision and aggressiveness of LNAV update sensor has deteriorated, and, and active in the route, the FMC is designed path tracking. subsequently, the computed navigation to maintain the centerline of the path. That n NPS — Provided data to the display system accuracy can no longer ensure basic operation has not changed since the system for lateral and vertical path containment (see fig. 4). original 767 FMC. deviation scales, deviation pointers, The FMC’s LNAV function continually and sensor performance indications. provides guidance to maintain the lateral Continued FMC modernization n RNP from the NDB — Enabled appli­ path centerline and any deviation from cation of RNP values coded in the NDB the path centerline is displayed as lateral The 737, 747-400, MD-80, and MD-11 for routes and procedures. cross-track error. In Boeing airplanes, cross- FMC functions that enabled RNP were

25 WWW.boeing.com/commercial/aeromagazine Figure 4: RNP in practice RNP defines the path and allowable tolerance for continuous operation (+ 1 RNP). Containment to ensure obstacle clearance is defined as + 2 x RNP. ANP less than the prescribed RNP provides position assurance for continued operation.

ANP containment radius

RNP and ANP displayed on the FMC CDU

ANP ≤1 x RNP for continued operation

Lateral boundary = 2 x RNP (airspace and obstacle)

As a result of these enhancements including enhanced safety, increased to reduce track miles, avoid noise-sensitive and additions to other FMC functions, the efficiency, reduced carbon footprint, areas, and reduce emis­sions through modern FMC is well-equipped for RNP and reduced costs. To fully realize these the use of efficient descent paths by operations that will enable future airspace benefits, operators may need to make minimizing terminal area maneuvering management concepts. changes to their airplanes and operations. (i.e., unwanted throttle move­ment) and The primary premise of a PBN system periodic altitude constraints. is to move away from restricted, sensor- The promise of PBN based operations to a performance-based Airspace modernization navigation system that incorporates PBN, which comprises both RNAV and RNP as the foundation and a system in RNP specifications, provides the basis for The current airspace system of airways which operational cost efficiencies are global standardization, which will facilitate and jet routes has not changed significantly empha­sized (see fig. 5). According to the future airspace design, traffic flow, and since the inception of non-directional International Civil Aviation Organization improved access to runways. This change beacons and VORs in the middle of the Performance-Based Navigation Manual, offers a number of operational benefits, last century. Incremental improvements, airspace procedures should be designed

26 aero quarterly qtr_02 | 09 Figure 5: Benefits of PBN These actual traffic plots at a major airport demonstrate the efficiencies that can be realized when a PBN design is implemented. Track miles can be significantly reduced through reduced vectoring, saving time, fuel, and emissions. Additionally, convective weather, restricted airspace, and noise-sensitive areas can be avoided using either designed procedures or dynamic rerouting.

27 WWW.boeing.com/commercial/aeromagazine such as RNAV en-route waypoints, RNAV structure, procedure design, and traffic 787 and 747-8 airplanes. Although modern SIDs and STARs, FANS dynamic rerouting, control methodology will need to focus on in every respect, each of the FMCs is oper­ and Q-routes, have been implemented, but safety and efficiency if capacities are to ationally similar to the original 767 FMC the general structure of the airspace still increase at major airports and operators are of the early 1980s. To address system reflects historic ATC methods. able to maintain fuel costs within reason. complexity and enhance the operational In a direct contrast to the PBN approach, Concurrent with the airspace evolution, capability of the flight crew for the transition the increased traffic since the early 1990s the FMC will continue to require enhance­ to the Next Generation Air Transportation has necessitated more complex arrival and ments that either control or participate System, Boeing and its partners are departure procedures — procedures that with other onboard systems for new traffic investigating new flight management meth­ frequently inflict a penalty on fuel efficiency control methods. These methods include odologies that focus on flight path trajectory with an added consequence of increased time-based metering, merging and spacing, management and ease of oper­a­tion. Such potential for flight crew error. self-separation during continuous descent new systems will assist the flight crew in The PBN concept is centered on arrivals and/or during the final segment, managing the trip costs and contribute to operational efficiencies. Several successes automated dependent surveillance a safe conclusion to each flight. have already been realized. Procedure and broadcast, and cockpit display of traffic airspace designers in Canada and Australia information. New terminal procedures, such Summary have worked with operators to plan routes as a hybrid RNP procedure that terminates and terminal area procedures that reduce in an instrument landing system or a global Flight management systems have evolved track miles while addressing environmental navigation satellite system landing system to a level of sophistication that helps flight issues that are receiving increased scrutiny final and autoland, are already in the FMC’s crews fly commercial airplanes more safely by the public and government. Both repertoire. However, considerations to and efficiently, while enabling PBN through Europe and the United States are imple­ the associated flight mode annunciator application of RNP and the evolution to menting RNAV and RNP procedures. changes during the transition from FMC- future airspace management systems. based guidance to autopilot guidance on For more information, please contact short final and other crew distractions will Future Concepts Sam Miller at [email protected]. require attention. The new 787 and 747-8 Contributors to this article: John Hillier, FMCs are addressing some of these issues Advanced airspace environments include chief engineer, Flight Management Systems, and implementing enhancements that the FAA’s Next Generation Air Transpor­ Center of Excellence, Honeywell Aero­ position those models for future PBN tation System, which will transform the space; Robert Bush, software tech lead, operations. Additionally, each of the FMC current ground-based ATC system to 737 Flight Management Computer System, designs has incorporated growth options satellite-based, and Europe’s Single GE Aviation; John C. (Jack) Griffin, associate so that changes to the FMC can be made European Sky ATM Research (SESAR). technical fellow (retired), Boeing. with minimal impact to the FMC software. Migrating to these environments will Flight crews will see significant improve­ require fundamental changes to air traffic ments in speed, capability, and operation management methodology. The airspace of the 737 FMC and the new FMCs in the

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